An exhaust purifying member that purifies exhaust gas by trapping particulate matter (PM) in exhaust gas with a filter located in an exhaust passage has been employed for an internal combustion engine such as a vehicle diesel engine. In such an exhaust purifying member, the filter needs to be regenerated by removing particulate matter accumulated in the filter before the filter is clogged by accumulation of trapped particulate matter.
Japanese Laid-Open Patent Publication No. 2003-20930 discloses an exhaust purifying apparatus that eliminates particulate matter in the filter. In the exhaust purifying apparatus of the above publication, the filter supports a catalyst that promotes oxidization of particulate matter, and fuel is added to exhaust gas that flows into the filter. The particulate matter trapped in the filter is oxidized (burned) by adding fuel, and the filter is thus regenerated.
If fuel is added as described above when clogging is caused at an upstream side of the exhaust purifying member, the following problems are likely to occur.
If clogging occurs, the flow of exhaust gas becomes uneven at a section where the clogging has occurred. Therefore, fuel that was supposed to be burned at this section is burned downstream of the section. In this case, particulate matter that is accumulated at the downstream section or particulate matter remaining unburned from a PM elimination process, that is, residual particulate matter is abruptly burned, which excessively increases the temperature of the exhaust purifying member. As a result, for example, thermal degradation may occur.
The state in which clogging is caused at the upstream side of the exhaust purifying member includes a state in which clogging is caused at the upstream end of the exhaust purifying member and a state in which clogging is caused in an exhaust purifying catalyst located upstream of the exhaust purifying member.